How are hormonal effects on sexual behavior mediated at the level of individual neurons or neural circuits? As logical steps toward answering this question, the proposed research aims to achieve: 1) a description of the neural circuitry controlling female mating behavior in the golden hamster (Mesocricetus auratus) and, 2) analysis of the functions of particular parts of the circuitry. Several lines of evidence indicate that the septal area and particular regions of the medial hypothalamus play important parts in female mating behavior in the hamster. Autoradiographic data demonstrating estrogen-uptake in these areas indicate they may be targets for estrogen action on mating behavior. Lesion experiments will test the idea that the septal area and medial preoptic area (MPO) contain neurons involved in the tonic inhibition of the lordosis response. The lesion method will also be used to determine whether MPO neurons are crucial for the ultrasonic vocalizations emitted by female hamsters during mating encounters. Recent data indicate that structures in the medial basal hypothalamus (MBH) are critical for lordosis in the hamster. Experiments proposed here will: 1) describe the MBH connections critical for lordosis using microsurgical cuts; 2) determine whether basic changes in sensorimotor function underly lordosis deficits following MBH lesions; 3) determine whether electrical stimulation there will facilitate lordosis; 4) determine the hormonal sensitivity of the MBH for facilitating lordosis, by hormone implants directly into the area. An attempt will be made to describe neural pathways important for lordosis by combining functional and neuroanatomical analyses in the same animals. Functional data will be gathered by observing changes in behavior following electrical stimulation, lesion, or knife-cut procedures. Neuroanatomical analysis using the Fink-Heimer technique will follow. This combination of methods will allow correlation of a behavioral change with degeneration in particular pathways.